[If] one gathers up peah, and says: “Behold, this is for such and such a poor man” —- R' Eliezer says: He has acquired it for him; but the Sages say: He must give it to the poor man that is met first.  The leket, the shich'chah, and the peah of a non-Jew are liable to tithing, unless he declared [them] ownerless.